Amphiphilic Magnetic Particles Dispersed in Water and Oil for the Removal of Hydrophilic and Hydrophobic Microplastics.

The study explores the synthesis and versatile properties of amphiphilic magnetic particles (AMPs) achieved through sequential coatings. Modulating the hydrophobic content in the synthesis process allows for the formation of hydrophilic, amphiphilic, and hydrophobic magnetic particles, with stable AMPs synthesis achieved at a ratio of hydrophilic to hydrophobic portions of approximately 71 to 29%. These AMPs exhibited outstanding dispersion in both oil and water within an oil/water mixture. Polyethylenimine in the AMP primarily enhances the removal of hydrophilic microparticles and facilitates dispersion in water. On the other hand, octadecylamine is specifically designed for the effective elimination of hydrophobic microparticles and their dispersion in oil. AMPs demonstrated effective removal capabilities for both hydrophilic and hydrophobic microparticles in water as well as hydrophobic microparticles in 100% oil. Our approach is also suited for eliminating hydrophobic microparticles dispersed in small quantities of oil floating on large bodies of water in real-world situations.

Compressible Separator and Catalyst for Simultaneous Separation and Purification of Emulsions and Aqueous Pollutants.

Oily wastewater, a global environmental concern, demands efficient oil/water separation and pollutant removal. Our compressible separator and catalyst (CSC) balls, prepared through sponge etching and metal nanoparticle synthesis, exhibited efficient degradation of dyes of varying sizes, spanning a molecular weight range from 139 to 696 g/mol during the oil/water separation. Control over the distance between catalysts was achieved by incorporating Ag-Pt-Pd catalysts into the sponge skeleton and by adjusting the compression rates. The dispersion of the catalysts improved degradation efficiency for larger dyes, while concentrating the catalysts proved to be more effective for the smaller ones. By optimizing the compression rates of CSC balls, we successfully achieved the effective removal of emulsions of different sizes and precise control of flux. Our CSC ball-loaded system offers efficient and versatile solutions for concurrent separation and purification of emulsions and pollutants with potential environmental benefits.

A Janus branch filter for washing machines: Simultaneous removal of microplastics and surfactants.

Emerging pollutants, such as microplastics (MPs), are becoming a significant issue worldwide. The highest percentage of MPs released into the environment occurs through daily laundry. The average weight of dreg obtained from 5 kg of laundry was 1.26 g/kg. According to energy dispersive X-ray (EDX) and thermogravimetric analysis (TGA) analyses, the dreg consisted of MPs (78.3-89 wt%, organic elements: C/O) and alien materials (11-21.7 wt%, inorganic elements: Al/Fe/Ca, etc.). Thus, to reproduce the real environment, alien materials (Fe3O4 and CaCO3) were added to various types of model MPs in the presence and absence of sodium dodecyl benzenesulfonate (SDBS) to test MP removal. Hydrophobic and hydrophilic MPs were generated upon laundering, accounting for 55-59% and 41-45% of MPs, respectively. We provide a novel approach to design a laundry filter system for the simultaneous removal of SDBS and hydrophilic/hydrophobic MPs.

Nanostructured Materials for Water Purification: Adsorption of Heavy Metal Ions and Organic Dyes.

Chemical water pollution poses a threat to human beings and ecological systems. The purification of water to remove toxic organic and inorganic pollutants is essential for a safe society and a clean environment. Adsorption-based water treatment is considered one of the most effective and economic technologies designed to remove toxic substances. In this article, we review the recent progress in the field of nanostructured materials used for water purification, particularly those used for the adsorption of heavy metal ions and organic dyes. This review includes a range of nanostructured materials such as metal-based nanoparticles, polymer-based nanomaterials, carbon nanomaterials, bio-mass materials, and other types of nanostructured materials. Finally, the current challenges in the fields of adsorption of toxic materials using nanostructured materials are briefly discussed.

Hybrid Bead Air Filters with Low Pressure Drops at a High Flow Rate for the Removal of Particulate Matter and HCHO.

A tower air filtration system was designed in which bead air filters (BAFs) were actively rotated by a fan motor to remove particulate matter (PM) or HCHO gas. Three types of BAF, hydrophilic, hydrophobic, and hybrid, were prepared and compared for the removal of PM and HCHO gas. A tower air filtration system loaded with hybrid BAFs purified 3.73 L of PM (2500 µg/m3 PM2.5) at a high flow rate of 3.4 m/s with high removal efficiency (99.4% for PM2.5) and a low pressure drop (19 Pa) in 6 min. Against our expectations, the PM2.5 removal efficiency slightly increased as the air velocity increased. The hybrid BAF-200 showed excellent recyclability up to 50 cycles with high removal efficiencies (99.4-93.4% for PM2.5). Furthermore, hydrophilic BAF-200 could permanently remove 3.73 L of HCHO gas (4.87 ppm) and return the atmosphere to safe levels (0.41-0.31 ppm) within 60 min without any desorption of HCHO gas.

Solar-Driven Unmanned Hazardous and Noxious Substance Trapping Devices Equipped with Reverse Piloti Structures and Cooling Systems.

A solar-driven unmanned hazardous and noxious substance (HNS) trapping device that can absorb, evaporate, condense, and collect HNSs was prepared. The HNS trapping device was composed of three parts: a reverse piloti structure (RPS) for absorption and evaporation of HNSs, Al mirrors with optimized angles for focusing light, and a cooling line system for the condensation of HNSs. The RPS was fabricated by assembling a lower rectangle structure and an upper hollow column. The lower rectangular structure showed a toluene evaporation rate of 6.31 kg/m2 h, which was significantly increased by the installation of the upper hollow column (11.21 kg/m2 h) and led to the formation of the RPS. The installation of Al mirrors on the RPS could further enhance the evaporation rate by 9.1% (12.28 kg/m2 h). The RPS system equipped with an Al mirror could rapidly remove toluene, xylene, and toluene-xylene with high evaporation rates (12.28-8.37 kg/m2 h) and could effectively collect these substances with high efficiencies (81-65%) in an unmanned HNS trapping device. This prototype HNS trapping device works perfectly without human involvement, does not need electricity, and thus is suitable for fast cleanup and collection of HNSs in the ocean.

2D and 3D Bulk Materials for Environmental Remediation: Air Filtration and Oil/Water Separation.

Air and water pollution pose an enormous threat to human health and ecosystems. In particular, particulate matter (PM) and oily wastewater can cause serious environmental and health concerns. Thus, controlling PM and oily wastewater has been a great challenge. Various techniques have been reported to effectively remove PM particles and purify oily wastewater. In this article, we provide a review of the recent advancements in air filtration and oil/water separation using two- and three-dimensional (2D and 3D) bulk materials. Our review covers the advantages, characteristics, limitations, and challenges of air filters and oil/water separators using 2D and 3D bulk materials. In each section, we present representative works in detail and describe the concepts, backgrounds, employed materials, fabrication methods, and characteristics of 2D and 3D bulk material-based air filters and oil/water separators. Finally, the challenges, technical problems, and future research directions are briefly discussed for each section.

Special Issue: Smart Nanomaterials for Environmental Remediation.

Nanomaterials that can be reversibly or irreversibly changed in structures and properties by the influence of external chemical and physical stimuli are defined as smart nanomaterials [...].

An Active Absorbent for Cleanup of High-Concentration Strong Acid and Base Solutions.

There is significant interest in developing novel absorbents for hazardous material cleanup. Iron oxide-coated melamine formaldehyde sponge (MFS/IO) absorbents with various IO layer thicknesses were synthesized. Various other absorbents were also synthesized and compared to evaluate the absorption capability of the MFS/IO absorbents for strong acid (15%, v/v) and base (50%, m/m) solutions. Specifically, absorbent and solution drop tests, dust tests, and droplet fragment tests were performed. Among the various absorbents, MFS/IO absorbents possessing a needlelike surface morphology showed several unique characteristics not observed in other absorbents. The MFS/IO absorbents naturally absorbed a strong base solution (absorption time: 0.71-0.5 s, absorption capacity: 10,000-34,000%) without an additional external force and immediately absorbed a strong acid solution (0.31-0.43 s, 9830-10,810%) without absorption delay/overflow during absorbent and solution drop tests, respectively. The MFS/IO absorbents were also demonstrated to be ideal absorbents that generated fewer dust particles (semiclass 1 (ISO 3) level of 280 piece/L) than the level of a clean room (class 100). Furthermore, the MFS/IO absorbents were able to prevent the formation of droplet fragments and solution overflow during the solution drop test due to their unique surface morphology and extremely high absorption speed/capacity, respectively.

Remote-Controlled Magnetic Sponge Balls and Threads for Oil/Water Separation in a Confined Space and Anaerobic Reactions.

Magnetic sponges (MSs) and magnetic threads with hydrophilic and hydrophobic characteristics that can perform remote-controlled oil/water separation in a confined space and anaerobic reactions were prepared. For large amounts of water or oil, trainlike hydrophilic or hydrophobic MSs composed of more than three sponge balls moved as a group and quickly absorbed the water or oil droplets in oil or water by magnetic manipulation from outside of the tube. For the removal of heavy oils below the water in three-liquid multiphase solutions, the hydrophobic MS balls were moved to the heavy oil below the water, absorbed some of the heavy oil, and returned to the light oil layer to deliver the heavy oil by means of an external magnetic field. The mixed oils floating on the water were easily removed by a suction pump once the heavy oil had been completely delivered to the light oil layer via the round-trip process. Furthermore, our approach was demonstrated for use in an anaerobic reaction system due to the strong magnetic property that transfers the reactants/products, the porous structure providing a reaction site, and the prewetting ability containing the reactants/products of the MSs and the oil layer prohibiting oxygen contact.

NiCo2S4 Nanotrees Directly Grown on the Nickel NP-Doped Reduced Graphene Oxides for Efficient Supercapacitors.

In this work, we report a feasible fabrication of NiCo2S4 nanotree-like structures grown from the Ni nanoparticle (NP)-doped reduced graphene oxides (Ni-rGO) by a simple hydrothermal method. It is found that the presence of Ni NPs on the surface of the rGOs initiates growth of the NiCo2S4 nanotree flocks with enhanced interfacial compatibility, providing excellent cyclic stability and rate performance. The resulting NiCo2S4/Ni-rGO nanocomposites exhibit a superior rate performance, demonstrating 91.6% capacity retention even after 10,000 cycles of charge/discharge tests.

One-Step Synthesis of Environmentally Friendly Superhydrophilic and Superhydrophobic Sponges for Oil/Water Separation.

Environmentally friendly superhydrophilic and superhydrophobic sponges were synthesized using a one-step approach for oil/water separation. A superhydrophilic or superhydrophobic sponge (MFS/CC-DKGM or MFS/CC-PDMS) was synthesized by one-step coating of melamine formaldehyde sponge (MFS) with a mixture of calcium carbonate (CC) rods and deacetylized Konjac glucomannan (DKGM) [or polydimethylsiloxane (PDMS)]. The MFS/CC-PDMS showed excellent absorption capacity, which reached 52⁻76 g/g following immersion into various types of oil/water mixtures. Furthermore, the MFS/CC-DKGM and MFS/CC-PDMS exhibited excellent water- and oil-flux performances, which reached 4,702 L/m² h and 19,591 L/m² h, respectively, when they were used as filters. The MFS/CC-DKGM and MFS/CC-PDMS maintained their wettability characteristics relatively well after the chemical, thermal, and mechanical stability tests.

One-pot synthesis of layered double hydroxide hollow nanospheres with ultrafast removal efficiency for heavy metal ions and organic contaminants.

Herein, Mg/Fe layered double hydroxide (MF-LDH) hollow nanospheres were successfully prepared by a one-step thermal method. After the thermal treatment of MF-LDH nanospheres at 400 °C, the MF-LDH was converted into the corresponding oxide, Mg/Fe layered double oxide (MF-LDO), which maintained the hollow nanosphere structure. The MF-LDO hollow nanospheres exhibited excellent adsorption efficiency for both As(V) and Cr(VI), showing 99% removal within 5 min and providing maximum removal capacities of 178.6 mg g-1 [As(VI)] and 148.7 mg g-1 [Cr(VI)]. Moreover, it met the maximum contaminant level requirements recommended by World Health Organization (WHO); 10 ppm for As(V) and 50 ppm for Cr(VI) in 10 and 20 min, respectively. Furthermore, Au nanoparticles were successfully introduced in the MF-LDO hollow nanospheres, and the products showed a conversion rate of 100% for the reduction of 4-nitrophenol into 4-aminophenol within 5 min. It is believed that these excellent and versatile abilities integrated with a facile synthetic strategy will facilitate the practical application of this material in cost-effective wastewater purification.

Polyelectrolyte Brush-Grafted Polydopamine-Based Catalysts with Enhanced Catalytic Activity and Stability.

Three types of surface treatments, namely, polyethyleneimine (PEI) coating, short PEI (S-PEI) grafting, and long PEI (L-PEI) grafting, were performed on polydopamine (Pdop)-based catalysts to enhance their catalytic activity and stability. Brush-grafted catalysts were prepared by the stepwise synthesis of Au and short (or long) PEI brushes on Pdop particles (PdopP/Au/S- or L-PEI grafting). PEI-coated Pdop-based catalysts (PdopP/Au/PEI coating) were also prepared as non-brush-grafted catalysts. Among the surface-treated PdopP/Au catalysts, the brush-grafted catalysts (S-PEI and L-PEI grafting) exhibited excellent and stable catalytic performance because the brush grafting enabled the protection of the catalysts against harsh conditions, effective transfer of reactants to the catalysts, and confinement of reactants around the catalysts. The brush-grafted catalysts could also more effectively decompose larger dyes than the non-brush-grafted catalysts. The process-to-effectiveness of PEI coating is the best because the release of Pdop from PdopP/Au was moderately inhibited by the presence of only one layer of PEI coating on the PdopP/Au. Thus, this approach could be an alternative method to enhance the stability of PdopP/Au catalysts.

Surface Design of Separators for Oil/Water Separation with High Separation Capacity and Mechanical Stability.

A convection heat treatment that can replace existing chemical oxidation methods was developed for the preparation of hierarchically oxidized Cu meshes with various surface morphologies, representing a very simple and green route that does not involve toxic chemicals. Three types of Cu meshes [bumpy-like (BL) and short and long needle-like (NL) structures] exhibited similar separation efficiencies of 95-99% over 20 separation cycles, as indicated by their similar water contact angles (WCAs; 147-150°). However, these Cu meshes exhibited different flux behaviors. Excessively rough and excessively smooth surfaces of the Cu mesh resulted in increased resistance to flow and to a decrease of the penetration of oil. A surface with intermediate smoothness, such as the BL-Cu mesh, was necessary for high flux over a broad range of oil viscosities. Furthermore, a less rough surface was more suitable for the separation of highly viscous oil. Computational fluid dynamics (CFD) simulations were carried out to support our experimental results. The BL-Cu meshes also showed outstanding mechanical stability because of their low resistance to the flow of fluids.

Cube sugar-like sponge/polymer brush composites for portable and user-friendly heavy metal ion adsorbents.

Portable, non-toxic, and user-friendly sponge composites decorated with polyelectrolyte (PE) brushes were developed for the fast and efficient removal of heavy metal ions from waste water or drinking water. The polyacrylamide (PAM) and polyacrylic acid (PAA) brushes were grafted onto the sponge via "grafting-from" polymerization. For the polyethyleneimine (PEI) brush, "grafting-to" polymerization was used. A polydopamine (Pdop) layer was first coated on the sponge. Then, PEI was grafted onto the Pdop-coated sponge via a Michael addition reaction. The PEI-grafted sponge exhibited the best adsorption capacity and the fastest reaction rate of all the brushes due to the numerous adsorption sites of the PEI. The adsorption performance of two different PEI-grafted sponges depended on the molecular weight (MW) of the PEI. Simply by being dipped into a glass of water, non-toxic PEI-grafted sponge instantly removed the low concentration heavy metal ions, demonstrating a practical application for individual users.

A remote-controlled generation of gold@polydopamine (core@shell) nanoparticles via physical-chemical stimuli of polydopamine/gold composites.

We present the synthesis of polydopamine particle-gold composites (PdopP-Au) and unique release of Au@Pdop core@shell nanoparticles (NPs) from the PdopP-Au upon external stimuli. The PdopP-Au was prepared by controlled synthesis of AuNPs on the Pdop particles. Upon near infrared (NIR) irradiation or NaBH4 treatment on the PdopP-Au, the synthesized AuNPs within the PdopPs could be burst-released as a form of Au@Pdop NPs. The PdopP-Au composite showed outstanding photothermal conversion ability under NIR irradiation due to the ultrahigh loading of the AuNPs within the PdopPs, leading to a remote-controlled explosion of the PdopP-Au and rapid formation of numerous Au@Pdop NPs. The release of the Au@Pdop NPs could be instantly stopped or re-started by off or reboot of NIR, respectively. The structure of the released Au@Pdop NPs is suitable for a catalyst or adsorbent, thus we demonstrated that the PdopP-Au composite exhibited excellent and sustained performances for environmental remediation due to its capability of the continuous production of fresh catalysts or adsorbents during the reuse.

Polyelectrolyte-mediated hierarchical mesoporous calcium silicates: a platform for drug delivery carrier with ultrahigh loading capacity and controlled release behavior.

We have developed a facile method for the poly(allylamine hydrochloride) (PAH)-assisted synthesis of mesoporous calcium silicate hydrates (PAH-CS) with a large specific surface area (BET = 348.4 m2 g-1) and pore volume (Vp = 1.42 cm3 g-1). Tetraethyl orthosilicate (TEOS) was employed as a silicon source, which was rapidly hydrolyzed and reacted with the amine groups of PAH to form spherical SiO2 nanoparticles (PAH-Si). Subsequently, Ca2+ ions reacted with the silicate anions produced during the dissolution of SiO2 in basic media, leading to the formation of the highly porous 3D networks of PAH-CS that were synthesized only under optimized reaction conditions. The PAH-CS containing an excess of Ca2+ and NH3 + enriched the surfaces with a very high cationic charge (ζ = +65.66 mV)and resulted in an extremely high loading capacity for anionic drugs and proteins. Ibuprofen (IBU) and FITC-labeled bovine albumin (FITC-Albumin) were chosen as a model drug and model protein, respectively, to test the loading and delivery efficiencies of the PAH-CS carriers. The ultrahigh drug loading capacities (DLC) and their release patterns were investigated under controlled pH conditions. Strikingly, the highest DLC reported to date (IBU or FITC-Albumin/carrier (3.35 g or 1 g g-1) was achieved in this work. The PAH-CS had no cytotoxic effect on osteoblast-like MC3T3-E1 cell lines evaluated by the LDH (Lactate dehydrogenase) assay in supernatant medium. Furthermore, the PAH-CS carriers could be entirely transformed to hydroxyapatite after releasing the drug in simulated body fluid (SBF), indicating good bioactivity and biodegradability of the PAH-CS carriers.

Polyelectrolyte-triggered transformation of various types of AgBr microstructures into AgBr nanophotocatalysts with a single shape and size.

AgBr nanostructures with unified shapes and sizes were prepared using simple polyelectrolyte (PE) coatings on various AgBr microstructures that were prepared by mixing silver precursors with hexadecyltrimethylammonium bromide (CTAB) under controlled conditions. The AgBr microstructures (plates, rods, and wires), regardless of initial structures or sizes, transformed into cubic AgBr nanoparticles (CNPs) after only three PE coatings. The electrostatic interactions between the PEs and the CTAB in the AgBr microstructures are the crucial factors that control the shapes and sizes of the AgBr microstructures. During the PE coating, the AgBr microstructures were transformed and rearranged into AgBr CNPs with favorable catalytic faces that enhanced the photocatalytic activity. The size- and shape-controlled AgBr CNPs showed excellent photocatalytic performance for the degradation of methylene orange (MO) dyes under visible-light irradiation without deterioration even after multiple uses.

Controlled etching of internal and external structures of SiO2 nanoparticles using hydrogen bond of polyelectrolytes.

We have demonstrated a novel strategy for the synthesis of mesoporous silica nanoparticles (MSNPs) using a surfactant-free method under ambient conditions. By the simple addition of an amine-based polymer (polyethylenimine; PEI) with a high molecular weight to a silica nanoparticle (SNP) solution, two types of MSNPs, including rambutan-like MSNPs (R-MSNPs) and hollow MSNPs (H-MSNPs), were produced. The structural changes of the MSNPs were systematically studied using various reaction conditions (reaction time, molar ratio and molecular weight of PEI, etc.) and were observed using electron microscopic techniques. The formation mechanisms of both MSNPs were carefully investigated using XPS, Raman, and IR spectroscopies. Because the synthesized MSNPs are highly porous materials that contain internal organic/inorganic networks, we investigated the removal/adsorption properties of these MSNPs with respect to pollutants toward possible future use in environmental remediation applications. The H-MSNPs exhibited better environmental remediation capabilities relative to the R-MSNPs because PEI is present between the cobweb-like internal structures of the H-MSNPs, thereby providing a significant number of reaction sites for the adsorption of pollutants. The approach presented here can also be used as a direct method for the preparation of intraconnected networks within the substructures.